Finite element models (FEM) of cranial design (structure-function relationships) have played an important role in attempts to reconstruct the ecological niches of fossil hominins, but the morphological and functional complexity of the cranium make it a challenging place to look for dietary signals. The lower structural and developmental complexity of the mandible in comparison with the cranium suggests that it should provide a clearer functional link to feeding behaviour and diet, yet attempts to link diet to mandible morphology have had mixed success. Here we used a validated FEM of a rhesus monkey (Macaca mulatta) mandible to assess the effects on mandibular strain regimes of chewing on food items with varied material properties and of biting at different points along the toothrow. Chewing on items with different material properties and using different bite points elicit variation in strain regimes around the symphysis where strain magnitudes are high, but strain magnitudes in the corpora vary little with food type and are of lower magnitude than the symphysis. The lack of distinctive strain regimes in the macaque corpus during chewing suggests that symphyseal morphology might be more closely related to the kinds of food being chewed than corpus morphology. This suggests that different parts of the primate mandible might reflect variation in different aspects of feeding behaviour and ecology.